A safe energy supply calls for the protection of the energy feed as well as of the energy distribution. These requirements are preferably made of a cable system. Small-scale networks can also make use of a conductor bar distribution system.
Consequently, power circuit breakers and an associated triggering system are set in such a manner that, whenever necessary, for purposes of interrupting fault currents, only the power circuit breaker that is located directly upstream from the fault site is triggered. This selectivity limits to a minimum the area (the faulty electric circuit) that has to be interrupted in a fault scenario. All of the other components of the installation remain in operation. Here, the triggering times of series-connected protection devices have to be carefully coordinated with each other and the switching devices as well as the distribution systems (cable or bars) have to be capable of conducting the short-circuit current for the entire time during which the switching device is switched off, plus the delay time that is needed for the selectivity. One speaks of a selective staggering of the protection devices in this context.
Protection and selectivity requirements, especially in stand-alone installations, can be stipulated in local or regional classification or building regulations, which should be observed in each individual case.
Thus, for instance, it can be stipulated for a consumer network that, in installations that require a main current source to maintain a specific priority consumer, it is preferable that it be possible to divide a main supply line into at least two sections that are normally connected via switches or other approved means. To the extent possible, the connections of the generators and of the consumers coupled thereto should be uniformly distributed over sections of the main supply line. Similar regulations or requirements exist in the case of large industrial consumers, whereby, as a rule, they have drawn up their own regulations.
Groups of consumers, some of them also having generators configured as diesel aggregates, are connected to a supply line (e.g. main cable line or busbar). For purposes of electrically disconnecting at least two such groups so as to uncouple them from each other in a fault scenario, a disconnection point is created with a coupling switch. After the coupling switch opens (in a fault scenario), both partial sections of a supply line are electrically independent of each other.
The rated currents in supply lines in a consumer network that is relevant for the invention can reach values of more than 8000 A, which is the case, for example, because of the high energy demand at a voltage level of up to 690 V AC. This high energy density causes low-voltage switching devices to operate at the limit of their capacity; in particular, mention should be made here of the short-circuit switch-off capacity. The coupling switch has to be capable of reliably interrupting short-circuit currents of more than 100 kA. Conventional power circuit breakers are overtaxed by such requirements, so that there is a need to find alternatives for limiting short-circuit currents.
The extremely high current intensities that occur during short circuits have been mentioned. This means that the current-carrying elements (cables and/or conductor bars) have to be dimensioned for such intensities. Therefore, these elements need to have lines with commensurately large cross sections. As a consequence, investment costs for lines with large cross sections are high, especially in view of the rising market prices for copper.
Protection systems against short circuits for low-voltage installations have already been proposed and there has even been speculation about a complex system with supraconductive disconnector switches (German patent application DE 10349552 A1).
The above-mentioned considerations apply equally to the energy supply of consumer networks that are relevant for the present invention such as, for example, residential neighborhoods, automotive assembly lines or large industrial consumers. The energy distribution there can have the topology of a ring (full ring or partial ring); the feed into the supply lines takes place at the medium voltage level via transformers. Other topologies are likewise possible.
Examples of high-speed short circuiters are the following: short circuiters as short-circuit switches that switch via thyristors (German patent application DE 4438593 A1) or switches of the vacuum interrupter type (German patent application DE 4404074 A1). Some types of high-speed short circuiters are multiple short circuiters while others, in turn, can only be actuated one single time (one-time short circuiter).
European patent application EP 1052 665 B1 and international patent application WO 2000 62320 A1 describe high-speed short circuiters of the type of a pyrotechnically operated high-speed short circuiter. This high-speed short circuiter can trigger a short circuit within an actuating time of less than 3 ms. The pyrotechnical drive drives a metal bolt through the stack of connecting bars so that the phases are electrically and mechanically contacted with each other within the actuating time. Pyrotechnically driven high-speed short circuiters are one-time short circuiters that have to be replaced after every switching procedure. In a low-voltage installation, the removal of an actuated one-time short circuiter and the installation of a new one-time short circuiter can be carried out by a person who has received electrotechnical training.